This invention relates to apparatus for positively locking a butterfly valve disk in a closed position to assure safe conduit maintenance downstream of the valve.
Butterfly valves have enjoyed widespread use in a large number of industrial applications in view of their reliability, operational ease and relatively low-cost. Typically, a butterfly valve comprises a circular plate that is mounted for rotation about a diameter of the plate either on a pivot rod that extends through a bore formed in the plate or the plate may be formed with lugs extending outwardly from the periphery, again, along a diameter. At least one end of the pivot rod or the lug will be connected to a valve actuating device which, when operated, will rotate the plate on the pivot rod or the lugs to effect opening and closing of the valve. Where maintenance on the conduit downstream of the valve is being carried out, it is necessary that the valve be maintained in its closed position for economic and safety reasons particularly in large valve installations were workers enter the conduit to perform work internally.
In the past, it has been the practice to use one or more site employees to monitor the valve position and verify closure while downstream work takes place. Typically, positive closure relies entirely upon the resistance provided by the actuating device. Such precautions are not only costly but do not in all cases effectively guard against failure and leakage past the valve. In the case of toxic or similar fluids, should the valve fail, those monitoring the valve must act quickly to manually override the actuator to minimize any damage or injury.
The present invention provides an operator with a mechanical means to ensure that a butterfly valve disk or plate is positively locked while in the closed position. In many, if not all butterfly valve installations, the annular seal mounted in the conduit with which the valve plate cooperates, allows rotation of the plate in a prescribed direction relative to the higher pressure side of the valve installation. Thus, in one form of the invention, the valve locking mechanism of this invention will be a mounted to operate through the conduit wall on the lower pressure side of the butterfly valve, adjacent to the valve. The device includes a circular headpiece securely mounted on the end of a shaft which has a threaded portion that cooperates with a hand wheel to effect raising and lowering of the shaft by rotation about its longitudinal axis whereby the external threads of the shaft cooperate with the internal threads on the hand wheel. A restraining mechanism is provided to prevent rotation of the shaft while the hand wheel is rotated to move the shaft relative to the valve housing. With this arrangement, operation of the hand wheel extends the threaded shaft into the conduit to bring the headpiece to a proper radial position in the conduit so that after positioning of the shaft relative to the valve plate, the headpiece can be rotated by means of the shaft to bring it into contact with a side of the butterfly valve plate to thereby prevent opening of the valve plate. With this arrangement, effective locking and unlocking can be quickly and simply carried out.
The foregoing and other advantages of the present invention will become apparent as consideration is given to the following detailed description taken in conjunction with the accompanying drawings, in which: